SRST Translation Rule Questions

Unanswered Question
Jul 29th, 2010

Hi NetPro's -

We have about 15 field offices running on Cisco 2811's communicating via MGCP to CUCM 7.0.1. They are all configured for SRST in the event of a WAN outage, however I have a couple of questions regarding voice translation rules...

Are translation rules necessary to make generic outbound calls? Are they absolutely necessary for inbound calls? I can understand the need for translation rules for inbound calls, as to essentially make then plar to specific extensions from analog FXO ports. My understanding of outbound, however, is a bit less clear. If a field office reports they cannot make outbound calls when in CM Fallback mode (reorder tone), could translation patterns be the culprit? Would the test voice translation-rule be a good test against a random local or long distance number?

I appreciate any and all assistance. Thanks in advance,


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Felipe Garrido Thu, 07/29/2010 - 11:04


Translation rules are not always necessary in an SRST environment. It really depends on multiple factor include, the type of connection to the PSTN (ISDN, FXO, SIP), the dial-plan for the IP phones and the differences in inbound call handling when in CUCM vs. SRST mode.

Translation rules are more important for inbound calls. Especially if, within CUCM, translation patterns are in use. For inbound calls, translation rules are useful for redirecting calls from their original destination, which may not be available in SRST mode (think Unity, UCCX, Unity connection) to an IP phone of a receptionist so that the call can be handled.  For outbound calls, translation rules are typically used to modify the calling party number as the called party number can easily be modified using the configuration under the dial-peer, to strip or prepend digits.

If outbound calls are failing in SRST mode, then I would first check to see that the dial-peers are configured to route the call out the correct interface before suspecting translation rules.  For inbound calls, especially if the called party information does not match the extensions on the phones, I would suspect a translation rules issue.

Below is some additional documentation on this topic.

Hope that helps.



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